1. Field of the Invention
This invention generally relates to direct emission displays and, more particularly, to hybrid emissive displays made using both organic light emitting diodes (OLEDs) and inorganic LEDs.
2. Description of the Related Art
The currently dominant direct emitting display technology uses organic light emitting diodes (OLED) in an active matrix array. The technology has several strengths compared with liquid crystal display (LCD) technology including high efficiency and very high contrast ratio. The technology also has some notable weaknesses including a relatively high cost, sensitivity to moisture and atmospheric oxidation and, more importantly, the low efficiency and poor lifetime of the blue emitting OLED devices. Typical blue OLEDs may have a quantum efficiency of only 5% and a limited lifetime of a few thousand hours before the efficiency decreases to the point that blue emission is too low, as compared to red and green OLEDs. This is especially problematic where image burn-in may be caused by a static image such as an icon or menu bar.
By contrast, inorganic blue LEDs fabricated using gallium nitride (GaN) have a quantum efficiency upwards of 40%, lifetimes of 50-60,000 hours, and are impervious to oxidation by water or air.
It would be advantageous to substitute robust blue inorganic LEDs for the blue emitting OLED pixels in a display to improve the display reliability.